1. Field of the Invention
This invention relates to a photographic camera having a tiltable photocell lens assembly for providing a compensated field of view when the camera is located in a predetermined orientation relative to a scene to be photographed.
2. Description of the Prior Art
The present invention relates to a photographic camera having a photocell unit for varying the exposure of a film unit in accordance with the intensity of scene light measured thereby, and more particularly to such a unit which will provide a correction in the field viewed by the photocell unit when the camera is rotated 90.degree. to take advantage of dimensional differences in a rectangular film format vis-a-vis a square film format.
U.S. Pat. No. 3,442,191 discloses a camera having an optical system for confining the acceptance angle of a photosensitive element to an angle generally below the horizontal when the optical axis of the camera's lens is generally maintained along the horizontal, regardless of the angular orientation of the camera. In other words, the field of view and the acceptance angle remain substantially the same during rotation of the camera about its roll axis, i.e., about the camera's optical axis or one parallel therewith. In the '191 patent, the field of view of the optical system is determined by the shape of a meniscus of a liquid which partially fills a tube whose axis is parallel to the optical axis of the camera and which is located between the photosensitive surface of a photosensitive element and the scene.
In response to the rotation of the above-noted camera about its optical axis, the attitude of the meniscus and its shape remain unchanged because of the symmetry of the tube about its axis, thus stablizing the field of view in response to camera roll (rotation of the camera about its optical axis). In response to camera pitch (change in angle of elevation due to rotation of the camera about a pitch axis perpendicular to the optical axis of the camera), the stability of the field of view is dependent on the stability of the curvature of the meniscus since the meniscus acts as a lens located in front of the sensitive surface of the photocell. Unfortunately, it appears the shape of the meniscus changes as the elevation angle of the camera changes primarily because of the nonsymmetry of the tube about the pitch axis. As a consequence, the field of view shifts with any significant changes in the elevation angle of the camera as measured from the horizontal since the field of view is perturbed to the extent that the shape of the meniscus changes.
U.S. Pat. No. 4,185,903 discloses a photocell assembly which includes a pendulously mounted ring which provides a roll sensitive control that maintains the field of view of a photocell lens in a fixed position as its associated camera is rotated about its optical (roll) axis. Such an assembly required a substantially friction-free connection between the ring and its supporting structure thus adding to the cost of its construction.